A frequent refrain amongst those who don’t accept evolution by natural selection as fact is that no one has ever seen evolution happening. Now, several decades ago this was true and in the vast majority of cases it would happen to slowly for us to reasonably observe within a human lifetime. Today, however, we have many examples of evolution happening on human timescales and this week we discovered another. I particularly like this example because it also ties in anthropogenic global warming as well, a denialism of which seems to all too frequently go hand in hand with evolution denial.
Researchers from the state university of New York studied the populations of bees in the alpine environment of the Colorado Rocky Moutains. Here there is a species of high altitude bee, Bombus alteatus, that has a particularly long tongue that it uses to get at nectar in the long tubed plants of the region, these plants, though, have decreased in density by 70% in the past 40 years. Using specimens of the same species collected between 1966-1980 they discovered that today’s bees have a tongue that is 24% shorter than their older counterparts. That is a very rapid change in just 40 or so generations.
The researchers had four possible theories as to why this had happened.
- The body size of the bee as a whole had decreased and this was simply a function of that.
- Coevolution with floral traits, i.e. the tubes of the flowers had decreased in length and so the bees didn’t need to waste any effort on growing longer tongues anymore.
- Competition from sub-alpine invaders, i.e. an invasive species was having an effect such that a shorter tongue resulted in a greater chance of survival for the bees.
- Diminishing floral resources resulting in the bees having a less specialised tongue that allowed them to feed at a greater variety of flowers.
Option one was easy enough to rule out with a measuring tape, ditto number two. Bees hadn’t got smaller and plant tubes hadn’t got shorter. They couldn’t find any evidence of any new species in the vicinity and so they were left with option number four. Close observation of the bees revealed that they have indeed started to feed on a greater variety of flowers in the intervening decades and this is what drove their evolution. But why the change in behaviour?
Alpine plants don’t like the heat. They need cold nights and, ideally, for the minimum temperature in the summer to not exceed 3.25 degrees C, this is at a fairly high altitude remember. Due to global warming the number of years where this temperature was exceeded went up from 12% 40 years ago to 48% in recent years; hence the 70% decline in flowers in the area. Fortunately for the bees they seem able to adapt in time and there hasn’t been an unexpected decrease in their numbers (outside of the global bee population catastrophe of the last decade). Future work by the team will be to see if the long tubed flowers have faired worse than the other species in the area as their main pollinators abandon them.